Sludge Pump

ABSTRACT

The present invention is a sludge pump system which includes a means for monitoring operation of a sludge pump. The sludge pump includes a material cylinder and a piston moveable in the material cylinder. A pump drive moves the piston during working cycles which include a pumping stroke and a filling stroke. A pump valve mechanism connects the material cylinder to an outlet during pumping strokes and connects the material cylinder to an inlet during filling strokes. A means for monitoring operation of the pump is provided. The means for monitoring includes a means for sensing a first parameter related to operation of the pump drive, a means for sensing a second parameter indicative of operation of the piston, and a means for determining errors in the operation of the pump based upon the first parameter and the second parameter.

This is a continuation application of U.S. application Ser. No.08/033,877, filed Mar. 19, 1993, now U.S. Pat. No. 5,388,965, which is acontinuation-in-part of U.S. application Ser. No. 07/981,982, filed Nov.24, 1992, and which has issued as U.S. Pat. No. 5,257,912 which is adivisional application of U.S. application Ser. No. 07/595,457, filedOct. 10, 1990, and which has issued as U.S. Pat. No. 5,106,272. Priorityof the prior application is claimed pursuant to 35 USC § 120.

BACKGROUND OF THE INVENTION

The present invention relates to the transport of a stiff-pastymaterial. The invention relates in particular to a sludge transportsystem wherein a positive-displacement sludge pump conveys the sludgethrough a pipeline, with the amount conveyed per unit of time and thetotal amount of material conveyed being determined automatically.

In recent years sludge pumps have become increasingly widespread fortransporting sludges through a pipeline in municipal and industrialapplications. Sludge pumps offer a number of crucial advantages overworm or belt conveyors. Pumping sludge through a pipeline meansenclosing odors and thus a safe and secure work place. Sludge pumps aresuitable for transporting thick, heavy sludges for which belt or wormconveyors are virtually useless. This is particularly important when thesludges are to be dried and burned in an incineration plant. Thepipeline has little or no wear; it is much cheaper to maintain than wormor belt conveyors. The pump and pipeline take up less space and canconvey the material through changes of direction by simple elbows.Sludge pumps furthermore offer a reduction of noise compared tomechanical conveyors and also work more cleanly and without soiling.

On the one hand, numerous federal laws and regulations control theprocessing and dumping of sludges and require that the processorprecisely determine and record the amount of processed material.

On the other hand, since such pumps are increasingly used in complexplants, extreme availability is required. These plants include forexample sludge incinerating plants, coal power plants and certainfunctional processes. The sludge pumps form a part of the plant which isfrequently responsible for a complicated sludge flow and serves tosupply the sludge, feed the sludge into the sludge pump and possibly totransport and dose the sludge at a certain place in the plant. In suchand similar cases of application one generally wants to be able to planand carry out the maintenance and servicing of the crucial units ofthese parts of the plant in advance so as to prevent unexpectedbreakdowns. These requirements are of special importance when standbypump systems cannot be used e.g. due to excessive costs so that symptomsof imminent wear must be recognized in time.

SUMMARY OF THE INVENTION

The invention is based on the problem of providing a system which makesit possible to detect and report imminent functional defects orincipient wear by continuously determining the effective amount ofsludge conveyed per unit of time and thus also the volumetric fillfactor of the pump in comparison to the theoretical sludge pumping rate,and by constant functional monitoring.

This is done according to the invention substantially by linkingindicators of the hydrostatic pump drive and control elements withparameters of the sludge pump that are derived from the working cycle ofthe material piston in the material cylinder. By comparing the switchingfunctions of the hydrostatic drive with the piston cycles one candetermine deviations from set values and actual values which, when theyexceed or fail to reach a certain degree, herald or already identifyfunctional defects.

This applies equally to one-cylinder and multicylinder pumps, a specialfeature being that with two-cylinder sludge pumps comparisons canconstantly be drawn between successive, similar working cycles of thetwo cylinder units from the interplay between the feed pump and itshydraulic drive assembly.

The invention also permits useful analysis of the individual workingsteps within one or more successive working cycles of the particularcylinder unit under consideration, and with two-cylinder pumps alsocomparison with the corresponding working step of another similarcylinder with the aid of measurements and evaluations of deviationsbetween the set working steps and/or fixed, set values. This permitsconclusions to be drawn which display imminent or already existing signsof wear, and which can then be reported.

Available indicators or parameters are pressures, position messages ofend positions of the material piston, open and closed positions ofvalves and the end positions of the hydraulic control valves, as well aspositions of the quantity governor of the hydraulic pump and the timeintervals between the individual measuring points of the indicators andparameters.

Since a pump has the function of transporting a certain required amountof sludge it appears very important to determine the percentage fillcontinuously for each stroke and to monitor continuously its constancywithin a permissible tolerance.

Almost all conceivable disturbances such as wear, defects, valve stemfunctional defects, misadjustment of controllers, etc., have a directlydetrimental influence on the total throughput of the pump and oftenprimarily on the percentage fill.

Systems for determining the percentage fill are known per se, forinstance from the Applicant's U.S. Pat. No. 5,106,272. However theyshall be briefly explained here again for the sake of completeness dueto the linkage with other parameters and indicators.

The percentage fill or volumetric efficiency results from the fact thatit is normally not possible to fill the cylinder to 100% of its knownvolume in positive-displacement pumps.

With pasty or even compact sludges or filter cakes a distance arisesbetween the filling piston and the column of sludge it draws in due tothe often low preliminary pressure on the filling side, and thisdistance becomes greater during the filling stroke. It becomes greaterthe higher the resistance to flow is in the material cylinder to befilled and the more gas pockets there are in the sludge.

In other words, the filling material piston moves ahead of the column ofsludge thereby producing between itself and the column of sludge anempty volume of varying size in which underpressure prevails but nosludge is present.

Thus, part of each discharging stroke of the pump involves only anelimination of this empty space and a compression of the sludge in thecylinder before the pressure of the piston overcomes the pressureprevailing at the outlet of the pump and conveys the material from thecylinder into the pipeline. Therefore, at least one working parameter ofthe pump is measured according to the invention in order to determinethe point during the pumping stroke at which the hydraulic pressure onthe piston suffices to overcome the outlet pressure and the sludgepasses out of the cylinder. This information is used to determine theactual volume that is conveyed during the pumping stroke. By adding thevolumes pumped during each stroke one obtains a volume sum. By dividingthe actually pumped volume during a working cycle by the time thisrequired one can determine an amount pumped during a certain period.

In a known embodiment the pump has an outlet valve between the cylinderand the outlet which opens when the pressure in the cylinder has reachedthe pressure at the outlet. The opening of the outlet valve is measuredand the period from opening of the outlet valve until the end of thepumping stroke is determined. The measured period is compared with thetotal period from the beginning until the end of the pumping stroke. Theresult is the fill factor as a percent of the total volume of thecylinder during each pumping stroke.

A further embodiment of the invention likewise uses a pump with anoutlet valve which opens when the pressure in the cylinder has reachedthe pressure at the pump outlet. A limit switch measures the position ofthe piston on the cylinder at the moment when the outlet valve opens.This represents information on the volume that is conveyed during agiven pumping stroke.

In a further embodiment the outlet valve of the pump is open during thetotal pumping stroke and the hydraulic pressure driving the piston ismeasured in comparison to the outlet pressure and either the time or thepiston position in the pumping stroke determined when the hydraulicpressure reaches the set outlet pressure. This can serve to determine apercentage fill or a volume which is conveyed during each pumpingstroke.

In a further embodiment the function of the hydraulic pressure isanalyzed to determine the time at which the rate of increase of thehydraulic pressure pattern approaches the value 0. This shows that thehydraulic pressure has risen so far that it corresponds to the pressurein the delivery pipe and the sludge is being pumped out of the cylinder.By determining either the linear position of the piston or the relativetime in which the rate of pressure increase becomes 0 and relating thisto the beginning and end of the pumping stroke, one determines thepercentage fill of the cylinder and thus the pumped volume during eachpumping stroke.

The above statements make it possible to provide accurate measurement ofthe particular pumping rate, the cumulative pumped volumes and thepumping efficiency according to the invention.

The inventive importance of detecting and monitoring further indicatorsand parameters is shown by the following.

The throttle valves in the hydraulic circuit of the pump drive are ofcrucial importance for the functioning of the inventive pump, i.e. thecorrect sequence of the switchover of the pump valves or pump gate viahydraulic valve and gate drives.

The chronological sequence of the changeover of the pump valves is alsocorrelated with the pistons in the material cylinders. The width ofopening of the throttle valves is thereby monitored such that thethrottle valves are neither open too far nor closed too far. This makesit possible for the open pressure or suction valve to close before thedirection of motion of the material pistons is switched over.

A further indicator that can be used is the hydraulic pressure in thehydrostatic pump drive. This pressure is correlated with the deliverypressure of the sludge transport. One can then determine preciselywhether the pump valves usually designed as poppet valves arefunctioning correctly or whether they show signs of wear.

Here, not only the functions of the sludge pump but also the functionsof the hydrostatic drive are monitored and any errors displayed. It istherefore possible to determine a particular functional defect in termsof whether it is in the units of the pump responsible for transport orin their hydraulic drive. However the correct functioning of the sludgepump does not depend only on the correct working of the units necessaryfor sludge transport and their hydrostatic drive. The usually desireduniform transport is also essentially dependent on the functioning ofthe sludge feed to the pump. This determines the correct materialcylinder fill. This can be checked and optionally displayed with thefeatures of the present invention. It is done substantially bydetermining any differences in the volumetric efficiencies of transportand their deviations from set limiting values.

On the other hand the correct functioning of the sludge pump is notdependent alone on the hydrostatic drive of its unit. Errors can alsoarise from energy losses occurring in the hydrostatic drive. Themonitoring of the sludge pump for such errors is possible with thepresent invention. Amounts of leaking oil, e.g. of the hydraulic pump,the control valves or the consumers, are determined that indicatefunctional errors as soon as they exceed a certain degree.

These amounts of leaking oil are of greater importance than thepressures that can be sensed. The features of the present invention makeit possible to determine roughly whether the hydraulic control valvesand the poppet/pump valves are reaching their set end positions, andthus to ascertain whether errors are occurring at these places. But sucha display can be suppressed when the hydraulic drive is impairedsimultaneously because the amounts of leaking oil are too great.

The hydrostatic drive of the sludge pump can of course function properlyonly if the pressure generator is functioning correctly. An embodimentof the invention, therefore also involves monitoring the pressuregenerator. This is done by comparing the set times of the piston travelin the material cylinder with the actual values.

The details, further features and other advantages of the invention arefound in the following description of embodiments of the invention withreference to the Figures in the drawings. Two-cylinder reciprocatingpumps are chiefly shown, which are also the object of the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective and broken away view, with certain portionsomitted, of a two-cylinder sludge pump system which uses inlet andoutlet popper valves,

FIG. 2 shows a perspective and partly broken away view of a portion ofthe two-cylinder sludge pump having a pivoting gate or transfer tubevalve,

FIG. 3 shows a graph of hydraulic pressure as a function of time in atwo-cylinder sludge pump as shown in FIG. 1,

FIGS. 4 to 7 show block diagrams of various display systems fordetermining individual and total volumes of sludge conveyed by the pump,

FIG. 8 shows a hydraulic circuit diagram for control of the sludge pumpof FIGS. 1 and 2,

FIG. 9 shows a time lapse diagram with time on the abscissa and pressureof the sludge over the functions of the throttle and control valves onthe ordinate,

FIG. 10 shows a time lapse diagram with time on the abscissa andhydraulic pressure of the hydraulic drive of a sludge pump controlledwith poppet valves on the ordinate,

FIG. 11 shows for comparison a representation, corresponding to FIG. 9,of the fluid pressure pattern over time for a gate-controlledtwo-cylinder sludge pump, and

FIG. 12 shows a bar chart for the diagram of FIG. 9.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a two-cylinder hydraulically driven sludge pump 10. Ahigh-solids sludge either held in a hopper 1 or fed via a continuoustransporter 314 passes inlets 12, 14 and is pumped through outlet 16into a pipeline (not shown). Pump 10 includes a pair of rigid cylinders18, 20 in which a pair of fixed pistons 22, 24 reciprocate. Inlet poppetvalve 26 controls the flow of sludge from inlet 12 into cylinder 18.Similarly, poppet valve 28 controls the flow of sludge from inlet 14into cylinder 20. The flow of sludge from cylinders 18, 20 to outlet 16is controlled by poppet valves 30, 32.

Inlet popper valves 26, 28 are controlled by hydraulic inlet poppervalve drive cylinders 34, 36. Outlet poppet valves 30, 32 are operatedby hydraulic outlet poppet valve drive cylinders 38, 40.

In the position shown in FIG. 1, inlet poppet valve 26 and outlet poppervalve 32 are open. Piston 22 therefore moves away from popper valvehousing 42, while piston 24 runs toward poppet valve housing 42. Sludgeis drawn through inlet 12 into cylinder 18, while sludge is pumped fromcylinder 20 into outlet 16.

Material pistons 22, 24 are connected to hydraulic drive pistons 44, 46which move in hydraulic cylinders 48, 50. Hydraulic fluid is pumped fromhydraulic pump 52 through high-pressure line 54 to control valve block56. Control valve block 56 includes two spool valves 56a, 56b whichcontrol the sequencing of high- and low-pressure hydraulic fluid tohydraulic cylinders 48, 50 and to poppet valve drive cylinders 34, 36,38, 40. Low-pressure hydraulic fluid flows from valve block 56 back tohydraulic reservoir 58 through low-pressure line 60.

Forward and rear switching valves 62, 64 signal the position of piston46 at the forward and rear ends of travel and are connected to controlvalve 56a. Each time piston 46 reaches the forward or rear end of itstravel in cylinder 50 a valve sequence is initiated which acts on allfour poppet valves so that they change from the occupied position to theopposite one, and reverses the high- and low-pressure connections tocylinders 48, 50, and whereby first only the valves that were openclose, leading to an intermediate state in which all four valves areclosed. The valves that were closed open only when the pressureconditions on the material pistons change accordingly at the start ofthe new pumping cycle. (Relief for the previously closed suction valveand loading for the previously closed pressure valve.)

The sequence of operations of pump 10 is essentially as follows.

As shown in FIG. 1, cylinder 20 discharges its sludge at outlet 16 whilecylinder 18 loads its sludge from inlet 12. At the end of the pumpingstroke material piston 24 is in the direct vicinity of poppet valvehousing 42 while piston 22 has reached its point furthest from valvehousing 42.

At this point valve 62 receives the signal that hydraulic drive piston46 has reached the forward end of its stroke. Valve slide 56a isactivated which causes all poppet valve drive cylinders to be actuated,whereby, as mentioned above, first only valve drive cylinders 34, 40 areactuated due to the prevailing pressure conditions. This causes inletpopper valve 26 and outlet valve 32 to close and thus attains the statein which all four poppet valves are closed.

At this point pistons 22, 24 are at the ends of their stroke and thus atthe point where their direction of motion is about to reverse.

All four poppet valves 26, 28, 30, 32 are closed. At the start of thenew stroke hydraulic pressure increases in cylinder 48, which drivespiston 44 forward. This moves piston 22 toward valve housing 42. Piston22 is now switched to its pumping or discharging stroke. At the sametime the hydraulic pressure prevailing forward of piston 44 istransferred from cylinder 48 through interconnection 66 to the forwardside of cylinder 50. This applies hydraulic pressure to the front sideof piston 46 to move it in a rearward direction. As a result piston 24begins moving away from housing 42 and performs its loading or fillingstroke.

When the effect of the opening pressure on drive cylinder 36 for inletvalve 28 on inlet 14 exceeds the effect of the pressure in cylinder 20,inlet valve 28 opens and allows sludge to flow through inlet 14 intocylinder 20 during the filling stroke.

When the piston moves forward it first eliminates the empty space thathas arisen and then compresses the sludge within cylinder 18. At themoment when the compressed sludge in the pumping cylinder equals thepressure of the compressed sludge in the delivery pipe at outlet 16,poppet valve 30 opens. Since the poppet valve for the dischargingcylinder opens only when the cylinder content has the same pressure asin the pipeline, no material can flow back.

The operation continues, with piston 22 moving forward and piston 24moving rearward until the pistons reach the end of their respectivestrokes. At that point switching valve 64 causes all four valve drivecylinders to be pressurized with the similar sequence as described abovefor the switching of valve 62.

The operation continues with one material piston 22, 24 operating in afilling stroke while the other is operating in a pumping or dischargestroke.

FIG. 2 shows a perspective view of a two-cylinder sludge pump 100 havinga pivoting gate or transfer tube valve (tube switch) 122 as opposed tothe poppet valve arrangement shown in FIG. 1. Pump 100 includes a pairof cylinders 102, 104 in which material pistons 106, 108 reciprocate.Hydraulic drive cylinders 110, 112 with drive pistons 114, 116 areconnected to material pistons 106, 108. Valve assembly 56 controls thesequencing of motion of pistons 114, 116 of the hydraulic drivecylinders, and thus the motion of pistons 106, 108 in material cylinders102, 104. Sludge is supplied to store tank 120 in which a pivotingtransfer tube 122 is positioned. Transfer tube 122 connects outlet 124with one of the two material cylinders (in FIG. 2 outlet 124 isconnected to cylinder 104), while the other material cylinder(in thiscase cylinder 102) is open to the interior of filling hopper 120. InFIG. 2 piston 108 moves forward in a discharge stroke to pump sludge outof cylinder 104 into outlet 124, while piston 106 moves rearward to drawsludge into cylinder 102.

At the end of a stroke hydraulic drive 126 which is connected to pivotarm 128 causes transfer tube 122 to swing so that outlet 124 is nowconnected to cylinder 102. The direction of motion of pistons 106, 108reverses, with piston 106 moving forward in a pumping stroke whilepiston 108 moves backward in a filling or loading stroke.

Hydraulic fluid to operate the cylinders and control pump 100 isproduced by a hydraulic pump and a drive assembly (not shown in FIG. 2)which is similar to pump 52 and drive assembly 52, 54, 58 shown in FIG.1.

The primary difference between pump 100 shown in FIG. 2 and pump 10shown in FIG. 1 is the valve arrangement. In pump 100 one of cylinders102, 104 is connected to outlet 124 during the entire discharge orpumping stroke. In contrast, in pump 10 outlet valves 30, 32 only openas soon as the material within the cylinder has compressed to a pressurelevel at which the outlet pressure and the pressure of material withinthe material cylinder are equal. As discussed later, the system of theinvention can be used with either pump 10 or pump 100, with somedifferences in the parameters being sensed to accommodate thedifferences in operation of the two valve assemblies.

FIG. 3 shows a graph of material pressure as a function of time in atwo-cylinder sludge pump of the type shown in FIG. 1. A pumping cyclestarts at point A, at which one of the pistons is at its forwardmostposition and the other piston is at its rearwardmost position. Asalready described above and particularly apparent from the wiringdiagram in FIG. 8, one of valves 62, 64 gives a switching pulse to spoolvalve 56a depending on the piston position. Said spool valve then clearsthe way for the opposite pressurization of the poppet valve drivecylinders and on the other hand provides a switching pressure pulse tospool valve 56b at a delay via throttle valves (X, Y) for oppositepressurization of hydraulic drive cylinders 48, 50.

The throttle valves should be set in such a way, i.e. delay theswitching of spool valve 56b to such an extent, that the valve cylinderoperation and the switching of spool valve 56b take place in directsuccession.

The sequence of operations starting at point A is essentially asfollows.

From A to B spool valve 56a switches. From B to C the two sludge poppetvalves that were open before first close and then spool valve 56bswitches, which means that at point C all four poppet valves are closedand the pistons in cylinders 48, 50 begin their motion in oppositedirections. That is, the cylinder which was filling before begins itspumping stroke and the other cylinder which was pumping before beginsits filling stroke. From C to D the still compressed sludge in the nowfilling cylinder is first allowed to at least partially decompressbefore the associated suction valve can open, and in the now pumpingcylinder there is a compression of the previously drawn-in sludgeapproximately to the level of the pipeline pressure, which leads toopening of this popper pressure valve. Strictly speaking, this poppetpressure valve opens somewhat earlier due to the additionally actinghydraulic pressurization of the poppet valve drive cylinder. But thisquantity is negligible. At point D until end E of the pumping stroke thesludge flows through the delivery pipe at constant pressure and atconstant velocity.

Operation of a pump of the type shown in FIG. 2 will produce a similargraph of material pressure versus time.

As shown in FIG. 3, total time T of a pumping cycle includes severaltime components relevant for determining the effectively pumped volumesand the percentage fill. Time T1 is the time from point A to point C,i.e. from the end of motion of the piston until the closing of thepoppet valves. Time T2 is the time from point C to point D, i.e. fromthe beginning of motion of the pumping piston until the pressure of thesludge in the cylinder has built to a point where it approximatelyreaches the outlet pressure so that the flow of material will be out ofthe cylinder into the outlet. Time T3 is the time from point D to pointE, during which material is being continuously pumped out of thematerial cylinder into the outlet.

A single-cylinder pump will have a similar type of curve, except thatthere will be a time period during which the piston is moving rearwardon a filling stroke and no pumping stroke is taking place. In atwo-cylinder pump (as considered here) of the type shown in FIGS. 1 and2 the material cylinders and pistons alternate filling and dischargingcycles so that there is always one cylinder and piston in a pumpingstroke while the other is in a filling stroke.

By comparing times T2 and T3 it is possible to determine a percentagefill of material in a cylinder during a particular pumping stroke. Thepercentage fill is:

    Percentage fill=T3/(T2+T3)

This assumes of course that the piston is moving at an essentiallyconstant velocity. By knowing the percentage amount of one pumping cycleand the total volume of this cylinder, the volume pumped during aparticular cycle can be determined. By adding together the pumpedvolumes for multiple cycles, an accumulated volume can be determined.

On the other hand, by knowing the entire volume of a time period overwhich that volume has been determined, an average pumping rate can becalculated. An instantaneous pumping rate for each cycle can also bedetermined. By knowing the total time T of a cycle, the percentage filland the total volume when the cylinder is 100% filled, the instantaneouspumping rate for each individual cycle can be determined.

FIG. 4 shows a first embodiment of the invention in which operation ofpump 10 is monitored by system 150 to provide an accurate measurement ofvolume pumped on a cycle-by-cycle basis and on an accumulated basis.Monitor system 150 includes digital computer 152, which in a preferredembodiment is a microprocessor including associated memory andinput/output circuitry, clock 154, output device 156, input device 157,poppet valve sensors 158, hydraulic pump swash plate position sensors160, and hydraulic system monitoring sensors 162.

Clock 154 provides a time base for computer 152. Although shownseparately in FIG. 4, clock 154 is, in a preferred embodiment of theinvention, contained as a part of digital computer 152.

Output device 156 takes the form for example of a cathode ray tube orliquid crystal display, a printer, or communication devices whichtransmit the output of computer 152 to another computer-based system,which may for example be monitoring the overall operation of facilitywhere sludge pump 10 is being used.

Sensors 158, 160, 162 monitor the operation of pump 10 and providesignals to computer 152. The parameters sensed by sensors 158, 160, 162provide an indication of the percentage fill of the cylinder during eachpumping stroke of pump 10 and allow computer 152 to determine the timeperiod of the cycle. From this information computer 152 determines thevolume of material pumped during that particular cycle, the accumulatedvolume, the pumping rate during that cycle, and an average pumping rateover a selected period of time. Computer 152 stores the data in memory,and provides a signal to output device 156 based upon the particularinformation selected by input device 157.

In one preferred embodiment of the invention the determination of volumepumped during a pumping cycle is as follows. Hydraulic system sensors162 provide an indication to computer 152 of the start of each pumpingstroke in pump 10. Sensors 162 also provide a signal as soon as thepumping stroke ends. These signals are supplied to computer 152 bysensors 162 preferably in the form of interrupt signals.

Poppet valve sensors 158 sense when the outlet valve is open during apumping stroke. The signal from poppet valve sensors 158 is alsopreferably in the form of an interrupt signal to computer 152.

Swash plate position sensors 160 on the hydraulic pump sense the flowrate of hydraulic fluid from the hydraulic pump. The swash plateposition determines the flow rate, and the output of position sensor 162can be an analog signal to computer 152 which cooperates with ananalog-to-digital converter, whereby the computer can convert it into aflow rate.

Based upon the signals from sensors 158, 160, 162 computer 150 knows thebeginning of each pumping stroke, the point in time when the outletpoppet valve opens, and the end of the pumping stroke. By using theclock signal from clock 154 computer 152 is able to determine times T2and T3. As long as the pumping rate is not changed by the operator inthe middle of a pumping cycle, the ratio of T3 to (T2+T3) will providean accurate representation of the percentage fill during that pumpingcycle. Swash plate position sensors 160 are intended to indicate tocomputer 152 whether the piston velocity has remained essentiallyconstant through the cycle. Otherwise, adjustments must be made becausethe ratio to determine the percentage fill is actually the ratio of thelength of pumping stroke with the material fully compressed to thelength of the total piston stroke. The use of times T2 and T3 instead ofthe end positions of the piston is therefore based on the assumptionthat the piston is moving at an essentially constant velocity.

In a preferred embodiment of the invention computer 152 calculates foreach stroke the percentage fill. Knowing the total displacement volumeof the cylinder, computer 152 calculates the actual volume pumped duringeach cycle. That volume is stored in a register within the memory of thecomputer. Computer 152 thereby updates the register which keeps anaccumulated total of volume pumped.

Because computer 152 also determines the length of time during eachcycle and the accumulated time over which the accumulated volume hasbeen pumped, it can calculate an instantaneous pumping rate for eachcylinder, as well as an average pumping rate over the accumulated time.

All four values (volume pumped in a particular cycle, total volume,instantaneous pumping rate, and average pumping rate) can be displayedby output device 156. Typically the operator will select the particularinformation to be displayed by providing a command through input device157 to computer 152.

FIG. 5 shows another embodiment of the invention in which display system200 shows the operation of pump 10. In this embodiment display system200 includes computer 202, clock 204, input device 206, output device208, pressure poppet valve sensors 210, and piston position sensors 212.

In the embodiment shown in FIG. 5, piston position sensors 212 sense theposition of each of the pistons of pump 10 during the pumping stroke.From the signals supplied by the piston position sensors the startingand stopping points of each pumping stroke are known. The signals fromthe piston position sensors are, in a preferred embodiment of theinvention, digital signals. For example piston position sensors 212 arepreferably linear position sensors, which may be analog sensors andcooperate with an analog-to-digital converter so that the signalsupplied to computer 202 is in digital form.

As soon as the pressure popper valve opens, as indicated by pressurepoppet valve sensor 210, the value being read by piston position sensor212 is supplied to the computer. The distance from the start of thepumping stroke to the opening of the pressure poppet valve is distanceL1, while the distance from the opening of the pressure poppet valve tothe end of the pumping stroke is L2. The percentage fill, in that case,is

    Percentage fill=L1/(L1+L2)

Clock 204 provides a time base to the computer so that the instantaneousand average pumping rate values can be calculated. As in system 150shown in FIG. 4, in system 200 of FIG. 5 the volume pumped during aparticular pumping cycle, accumulated volume pumped, instantaneouspumping rate, and average pumping rate are calculated by computer 202and stored in appropriate registers of its memory.

Upon commands supplied by input device 206 to the computer any or all ofthese calculated values can be displayed by output device 208. On theother hand, output device 202 can be a transmitter which sends theinformation to another computer of another system which is monitoringthe operation of a facility in which pump 10 is being used.

FIG. 6 shows a monitoring system 250 which is used to monitorgate-controlled pump 100 (shown in FIG. 2). Because there are no poppetvalves here in which to indicate the point at which pressure within thematerial cylinder equals the outlet pressure in pump 100, thisinformation must be obtained by sensing different parameters.

Monitoring system 250 includes computer 252, clock 254, input device256, output device 258, hydraulic pump pressure sensor 260, and outletpressure sensor 262. In this embodiment the computer receives analog ordigital signals from pressure sensors 260, 262. When the hydraulic pumppressure on the high-pressure side reaches a pressure that corresponds,with consideration of the piston area transmission ratio between thehydraulic drive cylinder and the material cylinder, to the outletpressure of the sludge which is sensed by outlet pressure sensor 262 orat a point downstream from outlet 124, the computer notes the timeduring the pumping cycle. It determines, at the end of the pumpingcycle, the ratio or percentage fill by dividing T3 by the sum of(T2+T3).

As in the embodiment of FIG. 4, system 250 assumes that the piston ismoving at a constant velocity during the pumping stroke. For furtheraccuracy, a swash plate position sensor similar to sensor 160 of FIG. 4can be added to system 250.

As with the embodiments shown in FIGS. 4 and 5, system 250 calculatesand stores volume during each cycle, accumulated volume, instantaneouspumping rate, and average pumping rate. That information is outputted byoutput device 258 upon command from input device 256.

FIG. 7 shows monitoring system 300 which monitors the operation of pump100. System 300 includes computer 302, clock 304, input device 306,output device 308, hydraulic pressure sensors 310, outlet pressuresensor 312, and piston position sensor 314. In this embodiment computer302 reads the position of the piston at the beginning of each pumpingcycle and at the end of each pumping cycle, and during the position andtime in which the hydraulic pump pressure from sensor 310 exceeds orequals the outlet pressure which is equivalent with consideration of thepiston area transmission ratio and which is sensed by outlet pressuresensor 312. System 300 calculates and stores the same information whichhas been described with regard to systems 150, 200, 250 in FIGS. 4 to 6.

Still other embodiments of the invention are possible. For example, bysensing pump pressure and determining the change of slope of thepressure curve shown in FIG. 3 it is possible to determine the pointwithin the cycle at which the pressure within the cylinder equals orexceeds the outlet pressure. By continually monitoring the hydraulicpump pressure and performing a slope analysis, an outlet pressure sensor(such as pressure sensor 312 shown in FIG. 7) is not necessary in someembodiments.

In conclusion, the methods/embodiments described above permit accuratevolume and pumping rate measurement of a sludge pump. The inventionrecognizes that in a positive-displacement sludge pump the fillingpercentage of the pumping cylinder can change from cycle to cycle. Bymonitoring the percentage fill on a cycle-by-cycle basis, highlyaccurate measurement of material delivered during each cycle,accumulated volume delivered, instantaneous pumping rate, and averagepumping rate can be provided.

Beyond what is described above, FIG. 1 shows that the sludge can notonly be supplied from store tank 1, 120 but also conveyed into inlets12, 14 by means of continuous transporter 314.

Continuous transporter 314 has in a certain embodiment, as shown, a pairof shafts 320, 322 which are equipped with cutters 324 for conveying thesludge toward inlets 12, 14 of pump 10. Shafts 320, 322 are driven byhydrostatic continuous transporter drive 326.

The continuous transporter drive is controlled by valve block 56 in theway described in the following.

When e.g. piston 24 moves toward valve housing 42 and pumps sludge intooutlet 16, and piston 22 simultaneously moves away from valve housing 42thereby drawing sludge into cylinder 18 via inlet 12, the continuoustransporter is in operation, i.e. it feeds sludge to inlet 12. When thepistons have reached their end positions the pumping stroke and thefilling stroke are at the end and the continuous transporter is stopped.Only when all valves are reversed, i.e. when the material pistons startrunning again, this time in the opposite direction, is the continuoustransporter switched on again.

The link between valve block 56 and continuous transporter drive 326 isshown schematically by broken line 350.

To make it easier to understand the inventive fully automatic integratedsludge pump control system described below, reference is first made tothe diagram in FIG. 9.

    ______________________________________                                        T.sub.10 = duration of cycle of cylinder 1 (pumping stroke) = AE              T.sub.20 = duration of cycle of cylinder 2 (pumping stroke) = EA              Point A: material piston reaches end position                                 Point B: spool valve 56 a has switched                                        Point C: all poppet valves have closed and directly there-                    after material pistons start in other direction,                              suction valve opens                                                           Point D: compression stroke is finished, pressure valve                       opens, flow of material begins from pump into de-                             livery pipe                                                                   Point E: like point A                                                         ______________________________________                                    

Functional sequence during the cycle time

    ______________________________________                                        AB:   spool valve 56a switches over                                           BC:   open poppet valves close and spool valve 56b then                             switches over                                                                 Note:                                                                         The reaching per se and the times when the poppet                             valves (in particular the pressure valve) reach their                         closed end positions and spool valve 56b reaches its                          end position are detected by the approach of the par-                         ticular pistons of the valves to proximity initiators                         as indicator pulses I1.sub.b or I2.sub.b (poppet pressure valves)             and I3 (spool valve 56b) and passed on to the computer                        for computation or possibly for correction of the                             throttle valve settings.                                                CD:   the pumping piston moves forward thereby compressing                          the previously drawn-in sludge to the pressure at the                         outlet of the pump, and the filling piston simultane-                         ously moves backward thereby relieving (decompressing)                        the sludge compressed by the previous pumping stroke,                         whereby the poppet suction valve opens.                                 DE:   the poppet pressure valve opens so that the effective                         pumping stroke runs.                                                          Note:                                                                         The time when the pressure valve begins to open is                            passed on to the computer as indicator pulse (the pis-                        ton moves away from the proximity initiator) I2.sub.a or                      I1.sub.a.                                                               ______________________________________                                    

Time intervals EF, FG, GH and HA are analogous to time intervals AB, BC,CD and DE, but for the other pump cylinder.

The corresponding pressure pattern of the hydraulic drive fluid is shownin the diagram of FIG. 9. When the pump is not controlled with poppetvalves but with a pivoting transfer tube or gate there is acorresponding pressure pattern that is shown in the diagram of FIGS. 10and 11.

However, the bar chart of FIG. 12 is more helpful for a betterunderstanding. It will therefore be referred to in the following.

The following parameters are thus determined as follows:

Volumetric efficiency ηvol total [%]

    ηvol.sub.1 =T.sub.13 /(T.sub.12 +T.sub.13)100 [%] (for cylinder 1)

    ηvol.sub.2 =T.sub.23 /(T.sub.22 +T.sub.23) 100 [%] (for cylinder 2)

    ηvol total=(ηvol.sub.1 +ηvol)/2

It is recommendable to correct values every two strokes.

Theoretical pumping rate Q_(theoretical) [m³ /h]

    Q.sub.theor =(n·v.sub.z ·60)/1000 [m.sup.3 /h]

wherein

V_(z) =piston-swept volume of one material cylinder of sludge pump in[dm³ ] (is inputted as fixed value depending on type of pump)

n=number of single strokes, i.e. indicator signals I₃, per minute

The piston-swept volume can be between about 3 and 1,000 liters (contentof material cylinder).

The numbers of strokes can be between about 0.5/min and 35/min.

The theoretical pumping rate is expediently calculated every twostrokes.

Determination of times T20, T21, T22, T23 or corresponding times offollowing stroke T10, T11, T12, T13

The theoretical total time of a stroke (T₂₀ or /T₁₀) can be calculatedfrom the amount of oil supplied by the hydraulic pump

    Q hydr.sub.theor [1/min]

and the consumed amounts of the differential or hydraulic cylinders (VD)and the total amount of switching oil (VS) (amount of switching oil) forcontrol valves 56a/56b and the poppet valve drive cylinders) as follows:

    T.sub.10 =T.sub.20 =((VD+VS)/Q hydr.sub.theor)·60 [sec]

For comparison the total time of a stroke is measurable and correspondsto the time between two functionally identical indications of twosuccessive strokes, e.g. between I1_(a) and I2_(a) =T20 or betweenI2_(a) and I1_(a) =T10.

Time T22, which corresponds to time T12, is measured as the timeinterval between pulses I3 and I2_(a) or I3 and I1_(a).

Time T21 or T11 is calculable from the ratio of the amount of oilconsumed for this period and the amount of oil consumed for the totalcycle. The amount of oil consumed for the total cycle is known from theabovementioned formula for calculating total time T20 or T10, namely

    Total amount of consumed oil=VD+VS

The amount of oil consumed in time T21 or T11 is only part of the totalamount of switching oil, namely VS₁, that is required for switchingcontrol valves 56a and 56b and closing two poppet valves. Theconsumption of the remaining amount of switching oil, namely VS₂, foropening the other two poppet valves falls within time interval T22 orT12.

The following relations thus hold for calculating times T21 or T11 witha hydraulic single-line circuit:

    Total consumption of switching oil=VS=VS1+VS2

    Differential cylinder oil consumption=VD

    Total oil consumption=VD+VS

    Oil consumption for partial cycle T21 or T11=VS1

It follows that:

    T.sub.21 /T.sub.20 =T.sub.11 /T.sub.10 =VS.sub.1 /(VD+VS)

    T.sub.21 =T.sub.20 ·(VS.sub.1 /(VD+VS) )

or

    T.sub.11 =T.sub.10 ·(VS.sub.1 /(VD+VS))

Since the oil consumption values for each machine are invariable valuesthey can be combined into a pump-specific factor

    f=VS.sub.1 /(VD+VS)

from which follows:

    T.sub.21 =T.sub.20 ·f

    T.sub.11 =T.sub.10 ·f

Factor f must be inputted for the particular type of pump used. TimesT23 or T13 are ultimately determined from the summation formulae

    T.sub.20 =T.sub.21 +T.sub.22 +T.sub.23

    T.sub.10 =T.sub.11 +T.sub.12 +T.sub.13

to

    T.sub.23 =T.sub.20 -T.sub.22 -T.sub.21

    T.sub.13 =T.sub.10 -T.sub.12 -T.sub.11

Remark: The process j poppet (pressure valve opens) reduces the strokerate of the material pistons, but this must be taken into account whencalculating T₁₃ * and T₂₃ * (the effective pumping times of the firstand second material cylinders in so far as a deduction must be made fromtimes T₁₃ /T₂₃ calculated above in accordance with the share of theconsumed amount of switching oil VS₃ for opening a poppet pressure valveover the total oil consumption for time range HA/DE determined above.

This time deduction is calculated from

    T.sub.23 *=T.sub.23 -ΔT.sub.23

    T.sub.13 *=T.sub.13 -ΔT.sub.13

whereby VS₃ must be inputted as the pump-specific value for theparticular type of pump used. It thus follows that:

    T.sub.23 *=T.sub.23 -ΔT.sub.23

    T.sub.13 *=T.sub.13 -ΔT.sub.13

Corrected times T₂₃ * and T₁₃ * can thus be used to calculate thevolumetric efficiencies

    ηvol.sub.1 and ηvol.sub.2

by being correlated with total running time TD of the differentialcylinder.

Therein,

    TD=(VD/Q hydr.sub.theor)·60 [sec]

so that:

    ηvol=(T23*/TD) or (T.sub.23 * /TD)·100 [%]

Influence of throttle valve adjustment

The correct adjustment of the throttle valves is of crucial importancefor correct measurement. At correct adjustment the actual time sequencecorresponds to the time sequence shown in the bar chart.

Throttle valves open too far

Spool valve 56b switches simultaneously with or even before the closingof the previously open poppet valves. The popper valves thus close onlywhen the pistons are already moving so that already pumped pumpingmedium flows back into the filling cylinder until the pressure valve isclosed.

The error of measurement can be recognized by pulse I1_(b) or I2_(b)(closing pressure valve) occurring only later than pulse I3 (reversingspool valve 56b and thus direction of material piston). Here a faultmessage must appear: "Throttle valves open too far".

Throttle valves closed too far

Spool valve 56b switches only much later than the closing of thepreviously open valves. The throttle pressure thereby becomes so highthat a check valve or safety valve (not shown) responds so that oilflows off to the tank. The time interval between pulse I2_(b) or I1_(b)and pulse I3 is measured. In a preferred embodiment, if a time portionf* of much more than f/2 is exceeded a fault message must appear:"Throttle valve closed too far". f* should be adjustable bypotentiometer between f/2 and 2f; a fixed value can possibly be inputtedafter presentation of test results with the sludge pump system of thepresent invention. First adjustment which triggers fault message whenreached: f*=f.

Measured values

As an indication of the total duration of a working cycle proximityswitches are used, as mentioned above, in the control block e.g. at bothends of spool valve 56b.

The standard proximity switches in spool valve 56b are also used formeasuring the number of strokes.

They provide signal I3 as a timer signal for total duration T₁₀ or T₂₀,the signal occurring at a time shortly after point C or shortly afterpoint G.

To indicate time D or H (beginning of discharge) a proximity switchsignal on one or the other pressure valve drive piston is used to signalthe beginning of opening of the particular pressure valve with I1_(a) orI2_(a) .

To indicate the correct adjustment of the throttle valves the closing ofthe pressure valve is used, as also mentioned above, and pulses I1_(b)or I2_(b) thereby compared to pulse I3.

Comparison of cylinder filling amounts

(by limiting factor X1 in percent)

If ηvol₁ is not equal to ηvol₂ a signal should be provided as soon asthe difference between the calculated values ηvol₁,2 for cylinder 1 andcylinder 2 is more than X1 in percent. X1 must be adjustable between 5and 50%. First adjustment X1=10%.

When given and preset limiting value X1 is impermissibly exceeded one ofthe following two signals is displayed:

"Suction valve 1: feed of medium impaired" and/or

"Suction valve 2: feed of medium impaired"

Which of the two material cylinders is impaired is recognized by thecomputer by the position of the particular pressure valves, e.g.

Suction valve 1 is impaired if pressure valve 1 stays closed longer thanpressure valve 2, i.e. T₁₂ >T₂₂

Suction valve 2 is impaired if pressure valve 2 stays closed longer thanpressure valve 1, i.e. T₂₂ >T₁₂

Cylinder filling impaired in both cylinders

(by limiting factor X2 in percent)

If the measured ηvol in both material cylinders falls below an adjustedvalue X2 that will be based on the particular existing operatingconditions, a signal should be provided for

    ηvol=((ηvol.sub.1 +ηvol.sub.2)/2)<X2

Feed of medium impaired

X2 is adjustable between 90% and 30%.

First adjustment: 70%

Hydraulic drive impaired

(too much leaking oil or potentiometer has come off)

The stroke rate of the material pistons of the pump is directlyproportional to pumping rate Q hydr_(theor) of the hydraulic pump. Itresults from the parameters of the particular type of sludge pump used.

If measured number of strokes n is much lower than number of strokesn_(theoretical), which corresponds to the amount of oil deliveredtheoretically by the hydraulic pump, the total amount of leaking oil istoo high.

The pumping rate of the hydraulic pump is measured by a potentiometer inthe adjusting drive for regulating the pumping rate of the hydraulicpump.

A balance during the trial run of the pump under pressure largelyeliminates the normal gap leakage.

If measured number of strokes n=X3×n_(theoretical), and X3 falls belowthe value of 0.85 (15% higher gap or leaking oil losses than in trialrun) a signal is provided:

"Check hydraulic drive system"

Value X3 must be available as a signal in percent for test purposes.

Poppet valve defective

If one of the poppet valves is defective, i.e. does not close properly,the delivery pressure in one stroke is much lower than in the othersince part of the pumped medium/sludge does not pass into the deliverypipe but flows back into the filling cylinder (if its pressure valve isdefective) or into the filling area (if the suction valve of the pumpingcylinder is defective). This reduces the flow rate in the delivery pipeand accordingly reduces the working pressure during this working stroke.

If the working or hydraulic pressure is lower in the pumping stroke ofcylinder 1 (2), the pressure valve of cylinder 2 (1) or the suctionvalve of cylinder 1 (2) is defective.

The computer compares the hydraulic pressure or the medium pressure(assuming corresponding sensors/e.g. pressure gauges) of two successiveworking strokes and provides the following signals:

    ______________________________________                                        "Pressure valve 2 or suction valve 1 defective"                               on the condition p1 ≦ X4 × p2                                    "Pressure valve 1 or suction valve 2 defective"                               on the condition p2 ≦ X4 × p1                                    ______________________________________                                    

where X4 is adjustable between 0.95 and 0.75.

First adjustment: 0.8

Remark

If the problem "too much oil leakage" occurs simultaneously, the signal"valve defective" must be suppressed since the differential cylinderpiston performing its pressure stroke probably then has higher oilleakage than the piston performing its filling stroke and poppet valveleakage is not the cause of the lower flow rate of the sludge in thedelivery pipe as the reason for the lower pressure.

Hydraulic drive of sludge pump defective

(higher ranked in interrogation than problem "too much oil leakage")

If T₁₀ and T₂₀ (duration of working cycles) have different values thisis an indication of

leakage in a differential cylinder, or

leakage in the switching elements, or

leakage on the valve drive cylinders

The computer then provides a signal:

"Wear of hydraulic components of sludge pump"

if the following conditions are met simultaneously:

the difference between T₁₀ and T₂₀ is greater than 10% and factor X5characterizing this difference is calculated as follows:

    T.sub.10 >T.sub.20 of T.sub.20 >T.sub.10

    X5=((T.sub.10 -T.sub.20)/T.sub.20)>10%

or

    X5=((T.sub.20 -T.sub.10)/T.sub.10)>10%.

the throttle valve position is normal

the cylinder filling difference is less than X1 in percent, i.e. normal

other fault messages are present, such as high oil leakage or valvedefective, but are suppressed in the display

X5 can be preset to 5-20%.

First adjustment: 10%

I claim:
 1. A method of monitoring operation of a pump for pumpingpartially compressible material, the pump having a first materialcylinder, a first piston movable in the first material cylinder, and apump drive for driving the first piston during working cycles whichinclude a first cylinder delivery stroke and filling stroke, the methodcomprising:sensing a first parameter which bears a known relationship toan actual volume of material displaced from the first material cylinderduring the first cylinder delivery stroke; determining a first cylinderfill efficiency based upon the sensed first parameter; and determiningerrors in pump operation based upon a comparison of the first cylinderfill efficiency with a comparison value.
 2. The method of claim 1,wherein the pump further includes an outlet valve which controlsmaterial flow from the first material cylinder to an outlet area, andfurther wherein the first cylinder delivery stroke includes acompression portion, in which the outlet valve is closed and materialwithin the cylinder is compressed, and a flow portion, in which theoutlet valve is opened and material is delivered from the first materialcylinder to the outlet area.
 3. The method of claim 1, furtherincluding:providing an error signal when the first cylinder fillefficiency is less than the comparison value.
 4. The method of claim 3,wherein the comparison value is approximately 30% to 90%.
 5. The methodof claim 3, wherein the pump further includes a second material cylinderhaving a second piston movable in the second material cylinder, thesecond piston being driven by the pump drive during working cycles whichinclude a second cylinder delivery stroke and a filling stroke, themethod further comprising:sensing a second parameter which bears a knownrelationship to an actual volume of material displaced from the secondmaterial cylinder during the second cylinder delivery stroke; anddetermining a second cylinder fill efficiency based upon the sensedsecond parameter.
 6. The method of claim 5, wherein the comparison valueis the second cylinder fill efficiency.
 7. The method of claim 6,further including:providing an error signal when the first cylinder fillefficiency exceeds the second cylinder fill efficiency by apredetermined amount.
 8. The method of claim 7, wherein thepredetermined amount is approximately 5% to 50%.
 9. A method ofmonitoring operation of a pump for pumping partially compressiblematerial, the pump having a first material cylinder, a first pistonmovable in the first material cylinder, a pump for driving the firstpiston during working cycles which include a first cylinder deliverystroke and a filling stroke, a second material cylinder, and a secondpiston movable in the second material cylinder, the second piston beingdriven by the pump drive during working cycles which include a secondcylinder delivery stroke and a filling stroke, the methodcomprising:sensing a first parameter which bears a known relationship toan actual volume of material displaced from the first material cylinderduring the first cylinder delivery stroke; determining a first cylinderfill efficiency based upon the sensed first parameter; sensing a secondparameter which bears a known relationship to an actual volume ofmaterial displaced from the second material cylinder during the secondcylinder delivery stroke; determining a second cylinder fill efficiencybased upon the sensed second parameter; determining a system fillefficiency based upon the first cylinder fill efficiency and the secondcylinder fill efficiency; and determining errors in pump operation basedupon a comparison of the system fill efficiency with a comparison value.10. The method of claim 9, wherein the system fill efficiency is anaverage of the first cylinder fill efficiency and the second cylinderfill efficiency.
 11. The method of claim 9, further including:providinga warning signal when the system fill efficiency falls below thecomparison value.
 12. The method of claim 11, wherein the comparisonvalue is approximately 30% to 90%.
 13. A method of monitoring operationof a pump for pumping partially compressible material, the methodcomprising:calculating a pump fill efficiency based upon a parameterwhich bears a known relationship to an actual amount of materialdisplaced from a cylinder of the pump; comparing the pump fillefficiency to a comparison value; and determining errors in pumpoperation as a function of the comparison of the pump fill efficiency tothe comparison value.
 14. The method of claim 13, wherein the pump has afirst material cylinder, a first piston movable in the first materialcylinder, and a pump drive for driving the first piston during workingcycles which include a first cylinder delivery stroke and fillingstroke; and further wherein calculating the pump fill efficiencyincludes:calculating a first cylinder fill efficiency of the firstmaterial cylinder based upon a parameter which bears a knownrelationship to an actual amount of material displaced during the firstcylinder delivery stroke.
 15. The method of claim 14, furtherincluding:providing an error signal when the pump fill efficiency isless than the comparison value.
 16. The method of claim 15, wherein thecomparison value is approximately 30% to 90%.
 17. The method of claim14, wherein the pump has a second material cylinder and a second pistonmovable in the second material cylinder, the second cylinder beingdriven by the pump drive during working cycles which include a secondcylinder delivery stroke and a filling stroke, the method furtherincluding:calculating a second cylinder fill efficiency of the secondmaterial cylinder based upon an actual amount of material displacedduring the second cylinder delivery stroke.
 18. The method of claim 17,wherein the comparison value is the second cylinder fill efficiency. 19.The method of claim 18, further including:providing an error signal whenthe first cylinder fill efficiency exceeds the second cylinder fillefficiency by a predetermined amount.
 20. The method of claim 13,wherein the pump has a first material cylinder, a first piston movablein the first material cylinder, a pump drive for driving the firstpiston during working cycles which include a first cylinder deliverystroke and a filing stroke, a second material cylinder, and a secondpiston movable in the second material cylinder, the second piston beingdriven by the pump drive during working cycles which include a secondcylinder delivery stroke and a filling stroke; and further whereincalculating the pump fill efficiency includes:calculating a firstcylinder fill efficiency of the first material cylinder based upon aparameter which bears a known relationship to an actual amount ofmaterial displaced during the first cylinder delivery stroke;calculating a second cylinder fill efficiency of the second materialcylinder based upon a parameter which bears a known relationship to anactual amount of material displaced during the second cylinder deliverystroke; and calculating the pump fill efficiency based upon an averageof the first cylinder fill efficiency and the second cylinder fillefficiency.
 21. The method of claim 20, further including:providing anerror signal when the system fill efficiency is less than the comparisonvalue.
 22. A method of monitoring operation of a pump for pumpingpartially compressible material, the pump having a first materialcylinder, a first piston movable in the first material cylinder, a pumpdrive for driving the first piston during working cycles which include afirst cylinder delivery stroke and a filing stroke, a second materialcylinder, and a second piston movable in the second material cylinder,the second piston being driven by the pump drive during working cycleswhich include a second delivery stroke and a filling stroke, the methodcomprising:sensing a first parameter which bears a known relationship toan actual pressure of material displaced from the first materialcylinder during the first cylinder delivery stroke; determining a firstcylinder delivery pressure based upon the sensed first parameter;sensing a second parameter which bears a known relationship to an actualpressure of material displaced from the second material cylinder duringthe second cylinder delivery stroke; determining a second cylinderdelivery pressure based upon the sensed second parameter; anddetermining errors in pump operation based upon a comparison of thefirst cylinder delivery pressure and the second cylinder deliverypressure.
 23. The method of claim 22, further including:providing awarning signal when the first delivery pressure exceeds the seconddelivery pressure by a predetermined percentage related to an error inpump operation.
 24. The method of claim 23, wherein the predeterminedpercentage is approximately 5% to 25%.
 25. A method of monitoringoperation of a pump for pumping partially compressible material, thepump having a first material cylinder, operation of which includes afirst cylinder delivery stroke and a first cylinder filling stroke, anda second material cylinder, operation of which includes a secondcylinder delivery stroke and a second cylinder filling stroke, themethod comprising:measuring a first cylinder cycle time of the firstcylinder delivery stroke; measuring a second cylinder cycle time of thesecond cylinder delivery stroke; and determining errors in pumpoperation based upon a comparison of the first cylinder cycle time withthe second cylinder cycle time period.
 26. The method of claim 25,further including:providing a warning signal when the first cylindercycle time exceeds the second cylinder cycle time by a predeterminedpercentage which bears a known relationship to an error in pumpoperation.
 27. The method of claim 26, wherein the predeterminedpercentage is approximately 5% to 20%.
 28. The method of claim 25,wherein the pump includes an inlet valve which regulates flow ofmaterial from a filling area to the first material cylinder, an outletvalve which regulates flow material from the first material cylinder toan outlet area, a valve controller which operates to control positioningof the inlet valve and the outlet valve, and a cylinder controller whichcontrols directional movement of a piston within the first cylinder; andwherein measuring the first cylinder cycle time includes:sensing a firstparameter which bears a known relationship to a first time period forthe valve controller to operate; sensing a second parameter which bearsa known relationship to a second time period for the first valve and thesecond valve to close; and sensing a third parameter which bears a knownrelationship to a third time period for the first piston to complete thedelivery stroke.